Haolong Liu

General characteristics of climate changes during the past 2000 years in China

The general characteristics of climate changes over the past 2000 years in China, regional differences and uncertainties were analyzed based on the recently peer-reviewed high time-resolution climatic reconstructions. The results showed that there exists four warm periods of the temperature variation in China since the Qin Dynasty, including the western and eastern Han Dynasties (200 BC-AD 180), the Sui and Tang dynasties (541–810), the Song and Yuan dynasties (931–1320), and the 20th century, and three cold phases involving the Wei, Jin, and North-South Dynasties (181–540), the late Tang Dynasty (811–930), and the Ming and Qing dynasties (1321–1920). The Song and Yuan warm period is consistent with the Medieval Warm Period over the Northern Hemisphere, and the cold phases of the North-South Dynasties and the Ming and Qing dynasties are paralleled to the Dark Ages Cold Period and the Little Ice Age, respectively. The 13th-15th century could be a shift to the wet condition of the climate, and the low precipitation variability is exhibited in western China prior to 1500. In the context of the climate warming, the pattern of the drought in north and flood in south is prevalent over the eastern China. In addition, the published reconstructions have a high level of confidence for the past 500 years, but large uncertainties exist prior to the 16th century.

Characteristics of Temperature Change in China over the Last 2000 years and Spatial Patterns of Dryness/Wetness during Cold and Warm Periods

This paper presents new high-resolution proxies and paleoclimatic reconstructions for studying climate changes in China for the past 2000 years. Multi-proxy synthesized reconstructions show that temperature variation in China has exhibited significant 50–70-yr, 100–120-yr, and 200–250-yr cycles. Results also show that the amplitudes of decadal and centennial temperature variation were 1.3°C and 0.7°C, respectively, with the latter significantly correlated with long-term changes in solar radiation, especially cold periods, which correspond approximately to sunspot minima. The most rapid warming in China occurred over AD 1870–2000, at a rate of 0.56° ± 0.42°C (100 yr)−1; however, temperatures recorded in the 20th century may not be unprecedented for the last 2000 years, as data show records for the periods AD 981–1100 and AD 1201–70 are comparable to the present. The ensemble means of dryness/wetness spatial patterns in eastern China across all centennial warm periods illustrate a tripole pattern: dry south of 25°N, wet from 25°–30°N, and dry to the north of 30°N. However, for all centennial cold periods, this spatial pattern also exhibits a meridional distribution. The increase in precipitation over the monsoonal regions of China associated with the 20th century warming can primarily be attributed to a mega El Ni˜no–Southern Oscillation and the Atlantic Multidecadal Oscillation. In addition, a significant association between increasing numbers of locusts and dry/cold conditions is found in eastern China. Plague intensity also generally increases in concert with wetness in northern China, while more precipitation is likely to have a negative effect in southern China.摘要本文综述了近来中国过去2000年气候变化研究中新取得的高分辨率代用资料和重建序列。结果显示: (1) 中国温度存在50–70年、100–120年和200–250年的准周期变化, 其年代和百年际变幅分别约为1.3℃和0.7℃, 且在百年尺度上与太阳辐射的长期变化显著相关, 尤其是气温寒冷阶段与太阳活动极小期相对应。 (2) 1870–2000年是中国增温最快的阶段, 速率为0.56 ± 0.42°C (100 yr)−1, 但20世纪的气温记录可能并不是过去2000年未曾出现过的, 重建表明公元981–1100年和1201–1270年间的温暖程度可与之相比。 (3) 对中国东部所有百年尺度暖期的集合平均显示其旱涝格局呈三极空间分布: 25°N以南偏旱, 25°–30°N偏涝, 30°N以北偏旱; 而在所有百年尺度冷期旱涝格局则呈经向分布。 (4) 强厄尔尼诺–南方涛动和北大西洋年代际振荡是导致20世纪中国季风区降水增加的主要原因。 (5) 在中国东部, 蝗灾与温度及降水变化显著相关, 干冷气候条件下蝗灾较多; 北部地区的鼠疫与干湿变化呈正相关, 但南方地区的鼠疫却与干湿变化呈负相关。

Phenological records in Guanzhong Area in central China between 600 and 902 AD as proxy for winter half-year temperature reconstruction

Phenological data obtained from historical documents constitute highly important ecological evidence for the pre-instrumental period, and can be used in analyzing climatic change in history. In this study, 87 phenological records about seasonality of non-biological events (e.g., first frost date), agriculture and ornamental plants (e.g., first flowering date) over 77 years were extracted from historical documents from the Sui and Tang dynasties in China to reconstruct the winter half-year (from October to next April) temperatures in the Guanzhong Area (located in central China) from 600 to 902 AD. Transfer functions between temperature and phenophases with significant correlations were established by using modern observation data. Temperatures from the study period were reconstructed by applying the transfer functions to historical phenological data. The reconstruction indicates that the winter half-year temperatures during 600–902 AD were 0.23°C higher than the reference period (1961–1990). The temperature changed with two distinct stages. During the 600s–800s, temperatures were approximately 0.38°C higher than at present but then temperatures decreased in the subsequent period (800–902 AD). These results are similar to ones from previous studies on the mean temperature and the divisions between warm and cold periods during the study period, though differences were found in the degree of warmness/coldness. This reconstruction provides a valuable contribution to a better understanding of climatic variability during the Sui and Tang dynasties in China.

Climate Change and Carbon Cycle

Climate change is often called changes caused by natural factors or human activities in terms of worldwide or regional, and it usually means a giant change or lasting a long time (≥10 years) on average and statistically, which includes changes in terms of mean value and change rate. Whereas, United Nations Framework Convention on Climate Change (UNFCCC) defines it as “climate change caused directly or indirectly by human activity’s changing the combination of the atmosphere after a long time of observation, apart from natural climate changes”. Although the two definitions differ a lot, now people mainly concern these climate change phenomenon: global warming in climate and ocean, frequency changes of extreme climate events, polar and mountain snow and glacier melting, lining up of the global ocean surface level, global precipitation changes in terms of time and space, increasing drought and flood, and other physical and chemical factors influencing global temperature and precipitation directly. Terrestrial ecosystem’s carbon cycle is the key to its material and energy cycle, and also a tie of geosphere–biosphere–atmosphere interaction. To deeply understand the carbon cycle’s process and mechanism is the basis to discuss ecosystem’s carbon management strategy and to analyze human’s progress in preventing and regulating global warming. This chapter systematically states our country’s research progress on climate change’s historical process in the first place, and then it makes comments on China’s carbon cycle study from several perspectives as the relationship between carbon cycle and climate change, carbon budget and its cycling mechanism, human activity’s influence on carbon cycle, global change’s influence on carbon cycle, etc. It then summarizes research progress in studying carbon cycle process, its influencing factors and global changing response from different perspectives of forestry, grassland, farmland, wetland, etc. Finally, it makes a comprehensive comment on our country’s technological progress in terrestrial ecosystem’s carbon-nitrogen-water flux observation technology and applications, which provides valuable information to China’s scientific research work, state-level carbon budget evaluation, and greenhouse gas management in the field of ecosystem carbon cycle.

Crop Yield and Temperature Changes in North China during 601-900 AD

Depending on the descriptions of crop yield and social response to crop failure/harvest from Chinese historical documents, we classified the crop yield of North China during 601–900 AD into six categories and quantified each category to be the crop yield grades. We found that the regional mean crop yield had a significant () negative trend at the rate of −0.24% per decade. The interannual, multiple-decadal, and century-scale variability accounted for ~47%, ~30%, and ~20% of the total variations of crop yield, respectively. The interannual variability was significantly () persistent across the entire period. The multiple-decadal variability was more dominant after 750 AD than that before 750 AD, while the century-scale variability was more dominant before 750 AD than that after 750 AD. The variations of crop yield could be partly explained by temperature changes. On one hand, the declining trend of crop yield cooccurred with the climate cooling trend from 601 to 900 AD; on the other hand, the crop yield was positively correlated with temperature changes at 30-year resolution with the correlation coefficient of 0.59 (). These findings supported that high (low) crop yield occurred in the warming (cooling) climate.